I. Field of the Invention
The present invention relates to a semiconductor apparatus for power switching and amplification.
II. Brief Description of the Prior Arts
Various types of compact high-performance power equipment and broadcast communication equipment have been recently developed using power semiconductor apparatuses. These fields require power semiconductor apparatuses having a high heat dissipation property and a high packaging density.
In order to decrease the size of semiconductor apparatuses and hence increase the packaging density thereof, heat dissipation becomes an important matter. It is very important to efficiently conduct heat of the semiconductor apparatus itself to a heat sink. The most efficient heat dissipation can be achieved by a thin package, and thus a semiconductor apparatus can withstand a higher power.
In a conventional power semiconductor apparatus, thermal expansion coefficients of basic components (i.e., a semiconductor device substrate, an insulator and a lead conductor) differ from each other. In particular, the insulator is brazed to the lead conductors by a silver brazing agent at a high temperature of 800.degree. C. or higher. For this reason, when the insulator is directly brazed to the lead conductors, a large warp occurs due to a residual stress caused by a difference between the thermal expansion coefficients of the insulator and the lead conductors. In the worst case, the insulator may crack, thereby degrading the hermetic state and lowering a dielectric strength voltage. In most cases, a thin ring or corrugated flanges are used as an intermediate damping member or members to damp the stress, and the insulator is brazed to the lead conductors through this intermediate damping member so as to damp or absorb the thermal stress.
High-speed switching of a large current is required in power semiconductor apparatuses. When switching control at high power is performed by a semiconductor apparatus having a low switching speed, a control frequency cannot be increased and falls within the audio-frequency range, thereby causing uncomfortable noise for workers. In addition, the semiconductor apparatus has a high switching loss, which causes difficulties in heat dissipation design of an equipment using this semiconductor apparatus.
No conventional high-power semiconductor apparatuses have satisfied the demand for high-speed switching of a large current. A conventional high-speed switching power semiconductor apparatus has been proposed, but this can switch only a small current. The structure of this conventional semiconductor apparatus is not suitable for high-speed switching of a large current of not less than 100 A, due to the high impedance of lead conductors.